Ketone peroxides are extensively used for the initiation of polymerization of ethylenically unsaturated compounds. Peroxides, however, have a tendency to be inflammable and exlosive, with some exhibiting these properties to a greater extent than others. These properties carry with them obvious hazards to the users of the materials as well as to the manufacturers.
Many suggestions have been made to reduce the inflammability of ketone peroxides, as discussed in more detail below, usually involving the incorporation of large quantities of water in the composition, the use of various additives and the use of particular solvents.
The apparent need to provide compositions of this sort has led to the widespread adoption of particular procedures for preparing such ketones. A commonly used procedure involves reaction of an aliphatic ketone, typically methyl ethyl ketone, in a solvent system under acid conditions with an aqueous solution of hydrogen peroxide, resulting in a two phase system. An excess of hydrogen peroxide over the stoichiometry to form the ketone peroxide is used in order to react as much of the ketone as possible.
The aqueous phase is separated from the organic phase and usually is discarded. The discarded aqueous phase contains unreacted hydrogen peroxide and possibly some unreacted ketone, and hence the discard of the aqueous phase results in an uneconomic use of these materials.
The organic phase contains a substantial proportion of water, typically about 10 to 15%, and the presence of such large amounts of water has disadvantages associated mainly with the end use of the peroxide material, since the water generally is incompatible with the organic components to be polymerized. The presence of water leads to bubbling in polymeric thin film formation.
In addition, the use of aqueous acids results in residual acidity in the organic phase which promotes continued reaction of the peroxide to higher oligomers. The trimer and higher oligomers are known to impart explosive properties to the composition. Therefore, the acidity has been neutralized, but the presence of commonly-employed neutralizing agents provides surface problems for the products of polymerization initiated by the peroxides containing such agents.
The prior art procedures for the production of aliphatic ketone peroxides therefore suffer from several drawbacks, which are sought to be overcome by the process which constitutes one aspect of the present invention.
In one aspect of the present invention, there is provided a novel process for forming aliphatic ketone peroxides, resulting in a product having superior stability, improved utility and decreased hazard.
As previously indicated there have been a number of prior art suggestions to provide safe ketone compositions, such as is described in U.S. Pat. No. 3,330,871 wherein it is indicated that a class of "Safety Solvents" for the ketone peroxide may be used to provide compositions which exhibit resistance to ignition and once ignited burn mildly. A wide variety of solvents are mentioned including various gylcols. However, it has been found that, while the compositions provided in the manner disclosed in this patent do indeed exhibit some resistance to ignition and once ignitied burn mildly, after burning for a period of time, which may vary widely depending on the solvent used and the quantity present, the composition suddenly flares up and burns vigorously. The tendency of these prior art compositions to flare up suddenly is extremely hazardous to a user or manufacturer seeking to extinguish the ignited composition, since while the ignited composition may be burning mildly and the operator can approach the flame with suitable extinguishing equipment, before extinguishing the flame, a sudden flare up may occur, causing injury to the operator.
In the second aspect of the present invention, there is provided a safe acyclic ketone composition which exhibits considerable resistance to ignition and when ignited burns in a controlled manner until all the peroxide composition has been consumed. Thus, the present invention avoids the flare up problem attendant the prior art compositions of U.S. Pat. No. 3,330,871.